Check for a disconnected or leaking vacuum hose between the engine and firewall. The mode doors are operated with vacuum motors. When a problem develops with the vacuum supply, the doors are spring-loaded to go to the defrost position for safety reasons. Your feet will freeze but you'll have a clear windshield.
If the air is cold, feel the radiator and heater hoses. They should be too hot to hold onto for very long.
Caradiodoc
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Monday, January 3rd, 2011 AT 3:33 AM